1. Field of the Invention
The present invention is directed to improved sorption cooling devices and methods for using sorption cooling devices. In particular, the present invention is directed to sorption cooling devices that are particularly adapted to maintain a reduced temperature within an enclosed container for an extended period of time. The cooling devices are particularly useful for temperature-controlled shipping containers that must maintain a temperature below ambient for extended time periods, such as from 1 hour to about 120 hours, or more.
2. Description of Related Art
The shipment of products that must have their temperature maintained within a specific range below ambient is one of the fastest growing market segments in the modern shipping industry. This growth is driven by a number of factors including widespread concerns about safety in the cold food distribution chain, increasing numbers of pharmaceutical and life sciences products which must have their temperature maintained within certain limits, the rapid growth in high-value specialty chemicals such as those used in the semiconductor industry, the increasing number of sophisticated medical tests which require the shipment of patient specimens to an external laboratory, the increased number of clinical trials associated with new pharmaceutical discovery and the increased delivery of products directly to the customer as a result of Internet ordering.
This field is generally referred to as controlled temperature packaging (CTP). CTP can be segmented by the target temperature range, namely: frozen (below 0xc2x0 C.); 2xc2x0 to 8xc2x0 C.; and less than ambient (e.g., less than 30xc2x0 C.). In addition, CTP may be segmented by container size, namely: greater than pallet; one cubic foot to pallet; and less than one cubic foot. Containers having a size greater than pallet are typically cooled by mechanical refrigeration and the shipment times are typically from days to many weeks. The one cubic foot to pallet size segment is dominated by systems using ice (e.g., gel packs) and/or dry ice as a coolant wherein the containers are insulated using expanded polystyrene (EPS). The market segment for containers less than one cubic foot in size is very limited due to an unmet need for a small, lightweight cooling mechanism.
Although many basic ice/EPS systems are in use, there is a wide variation in quality and performance of the packaging depending on the value of the product and the sensitivity of the product to temperature fluctuation. A relatively simple system includes a cardboard box into which EPS sheets have been cut and placed. The container is then filled with dry ice in which, for example, frozen fish is shipped. A more sophisticated approach is a validated system consisting of custom molded EPS forms in a rigid box with both frozen and warm gel packs, the combination of which has been tested through a range of temperature cycles for specified thermal properties. Such a validated system can be used for shipping pharmaceuticals. For example, many pharmaceutical products such as vaccines and antibodies must be maintained within a range of 2xc2x0 C. to 8xc2x0 C.
The existing ice/EPS cooling system is unsatisfactory for various reasons including: increased environmental concerns associated with the disposal of large quantities of EPS and gel packs; the high cost of shipping; and the required freezers at the shipping source to maintain the frozen packs. The high cost of shipping is directly related to the high volume associated with the EPS and the high volume and mass associated with the gel packs. For a one cubic foot box with a 60 hour lifetime at 2xc2x0 C. to 8xc2x0 C., over 90 percent of the volume is consumed by EPS and gel packs. Some reduction in volume and shipping costs may be obtained by using vacuum insulation panels (VIPs), but the high cost of VIPs has precluded significant market penetration.
An example of the foregoing system is illustrated in U.S. Pat. No. 5,924,302 by Derifield issued on Jul. 20, 1999. This patent illustrates a shipping container that includes a plurality of cavities adapted to receive a coolant (e.g., gel packs) that surround a cavity adapted to receive an item to be shipped.
Electrically cooled shipping containers are illustrated in U.S. Pat. No. 6,192,703 by Salyer et al., issued on Feb. 27, 2001. This patent discloses a portable refrigerator unit and storage container employing vacuum insulation panels and a phase change material. Phase change materials undergo a change in physical form (e.g., solid to liquid) thereby absorbing heat from the surrounding environment. A battery driven refrigeration system provides cooling of the shipping container.
The use of reactor-based rechargeable portable coolers are illustrated in U.S. Pat. No. 5,186,020 by Rockenfeller et al., issued on Feb. 16, 1993. This patent discloses a portable cooler utilizing a gas-liquid-gas phase change to effect cooling of chamber. However, the reactor-based apparatus disclosed by Rockenfeller et al. requires a source of electricity to effect the initial gas-liquid phase change. As a result, the apparatus occupies additional space and has additional weight, making it cost-ineffective and severely impairing its utility either for a single-use basis or for a shipping container.
A sorption cooler is illustrated in U.S. Pat. No. 5,048,301 by Sabin et al. This patent discloses a sorption cooling unit where the cooling liquid is maintained in the evaporator prior to the sorption process. A disadvantage of this device is that too much energy is consumed by having to cool the cooling liquid in the evaporator upon activation of the sorption unit. Space is also wasted in that the evaporator will require a relatively large volume to enable an efficient evaporation process because both the liquid and evaporation volume are located in the same general space. Furthermore, space limitations restrict the amount of cooling liquid that may be maintained in the evaporator.
Thus, there is a need for a temperature-controlled container, such as a shipping container, having a lightweight cooling device that does not occupy a large volume. It would also be advantageous if the temperature of the container was controllable over a range of temperatures. It would also be advantageous if the cooling device had the ability to maintain the reduced temperature for an extended period of time. It would also be advantageous if the cooling device could be used cost effectively on a single-use basis.
The present invention is directed to sorption cooling devices and temperature-controlled containers incorporating sorption cooling devices, particularly temperature-controlled shipping containers for the transportation of temperature sensitive products.
The sorption cooling devices according to the present invention provide numerous advantages over sorption cooling devices utilized in the prior art. According to one embodiment, a sorption cooling device includes a liquid supply apparatus that is responsive to changes in the ambient temperature. The apparatus includes a rigid housing, a first flexible pouch disposed within the rigid housing that contains a high vapor pressure substance, a second flexible pouch enclosing a supply liquid and disposed within the rigid housing adjacent to the first flexible pouch and a liquid conduit for providing liquid communication between the second pouch and an evaporator. The high vapor pressure substance causes the first flexible pouch to exert pressure on the second flexible pouch and assist in the flow of liquid from second flexible pouch to the liquid conduit. Increases in temperature increase the vapor pressure within the first flexible pouch, thereby increasing the flow rate of the liquid and the cooling rate.
According to another embodiment, a sorption cooling device is provided that includes absorber, and evaporator, a vapor passageway disposed between the evaporator and absorber to direct vapor from the evaporator to the absorber and a reservoir adapted to supply refrigerant liquid to the evaporator. The reservoir includes a rigid housing, a first flexible pouch disposed within the rigid housing and enclosing a high vapor pressure substance, a second flexible pouch disposed within the rigid housing and adjacent to the first flexible pouch that encloses a refrigerant liquid and a liquid conduit for providing liquid communication between the second flexible pouch and the evaporator. The high vapor pressure substance causes the first flexible pouch to exert pressure on the second flexible pouch to assist in the flow of refrigerant liquid from the second flexible pouch to the liquid conduit.
According to another embodiment of the present invention, a sorption cooling device is provided including an evaporator, an absorber adapted to absorb vapor from the evaporator, a first reservoir adapted to contain a first refrigerant liquid, a second reservoir adapted to contain a second refrigerant liquid, means for supplying liquid from the first reservoir to the evaporator at a first liquid flow rate and means for supplying liquid from the second reservoir to the evaporator at a second liquid flow rate, wherein the first liquid flow rate is faster than the second liquid flow rate. The first reservoir can quickly provide the evaporator with refrigerant liquid to initiate cooling while the second reservoir maintains the cooling over an extended period of time.
According to yet another embodiment of the present invention, a method for operating a sorption cooling device is provided. The sorption cooling device includes an evaporator and absorber. A first portion of liquid is provided to the evaporator and a first liquid supply rate and a second portion of liquid is provided to the evaporator at a second liquid supply rate that is lower than the first liquid supply rate. This enables the sorption cooling device to rapidly cool during an initial stage and maintain cooling over an extended period of time.
According to another embodiment of the present invention, a sorption cooling device is provided that includes an evaporator for providing cooling, absorber adapted to absorb vapor formed in the evaporator, at least first reservoir adapted to contain a refrigerant liquid and supply the refrigerant liquid to the evaporator, a refrigerant liquid disposed in the first reservoir and a flow restriction device disposed between the refrigerant liquid and the evaporator to restrict flow of refrigerant liquid to the evaporator. By restricting the flow of liquid to the evaporator, the cooling provided by the sorption cooling device can be extended over a long period of time.
According to another embodiment of the present invention, a sorption cooling device is provided that includes an evaporator for providing cooling, absorber adapted to absorb vapor formed in the evaporator, a liquid reservoir adapted to contain a refrigerant liquid and supply the liquid to the evaporator and a freezing point suppression agent within the evaporator that is adapted to lower the freezing point of the refrigerant liquid when the refrigerant liquid is fed to the evaporator. Examples of useful freezing point suppression agents include salts sodium chloride, calcium chloride and similar salts.
According to another embodiment of the present invention, a sorption cooling device is provided that includes an evaporator for providing cooling, an absorber adapted to absorb vapor formed in the evaporator and vapor passageway adapted to permit vapor flow from the evaporator to the absorber. The vapor passageway includes a thermally insulating material heading a thermal resistance of at least about 2.8 K.m2/W. Accordingly, heat generated in the absorber is thermally isolated from the evaporator, enhancing the cooling capability of the sorption cooling device.
According to another embodiment of the present invention, a sorption cooling device is provided including an evaporator having a cooling surface, an absorber adapted to absorb vapor formed in the evaporator and a vapor passageway disposed between the evaporator and absorber. The absorber includes a desiccant and a thermally conductive material disposed within the desiccant, wherein the thermally conductive material has a higher thermal conductivity than the desiccant. The higher thermal conductivity material enhances the ability of the absorber to transfer heat away from the evaporator, thereby enhancing the cooling ability of the sorption cooling device.
The present invention is also directed to temperature-controlled containers incorporating sorption cooling devices, such as temperature-controlled shipping containers. According to one embodiment, a temperature controlled container is provided that includes a bottom container portion having a bottom wall in at least a first sidewall defining a cavity adapted to contain a product therein. A top container portion includes a top surface and a bottom surface and is adapted to combine with a bottom container portion to define a product cavity, the top container portion forming the top wall of the container. A sorption cooling device is disposed in the top portion wherein the cooling surface of the evaporator is adapted to provide cooling to the product cavity.
According to another embodiment of the present invention, a temperature-controlled shipping container is provided that includes at least a sidewall and top and bottom walls defining a cavity adapted to contain a product within the cavity. A sorption cooling device is incorporated in the container that is adapted to cool the cavity. The sorption cooling device includes an evaporator in thermal communication with the cavity, an absorber adapted to absorb vapor formed in the evaporator, a vapor passageway disposed between the absorber and evaporator and a reservoir adapted supply refrigerant liquid to the evaporator wherein a vapor pressure within the reservoir causes the flow rate of refrigerant liquid to increase in response to an increase in ambient temperature. The reservoir can include a rigid housing, a first flexible pouch disposed within the rigid housing and enclosing high vapor pressure substance within the first flexible pouch and a second flexible pouch disposed within the rigid housing adjacent to the first flexible pouch and enclosing a refrigerant liquid. A liquid conduit is provided for liquid communication between second flexible pouch and the evaporator. The high vapor pressure substance causes the first flexible pouch to exert pressure on the second flexible pouch to assist the flow of refrigerant liquid to the liquid conduit.
According to another embodiment, a temperature controlled container is provided that includes a container heading at least a sidewall and top and bottom walls defining a cavity adapted to contain a product therein, the sorption cooling device having an evaporator, an absorber and a vapor passageway disposed between the evaporator and the absorber wherein the evaporator is disposed in thermal communication with the cavity to provide cooling to the cavity and a liquid reservoir adapted to provide liquid to the evaporator upon activation of the sorption cooling device.
According to another embodiment, a temperature-controlled shipping container is provided that includes an insert having top, bottom and sidewalls defining a cavity within the insert and a sorption cooling unit incorporated in the insert wherein the sorption cooling unit includes an evaporator positioned adjacent to the cavity to provide cooling to cavity. A container substantially encloses the insert.
According to another embodiment of the present invention, a temperature controlled shipping container is provided that includes a container having at least sidewall and top and bottom walls defining a cavity that is adapted to contain a product therein. A sorption cooling device is incorporated in the temperature-controlled shipping container that includes a liquid reservoir, an evaporator in thermal communication with the cavity to provide cooling to the cavity, an absorber which is thermally isolated from the cavity and means for supplying liquid from the reservoir to the evaporator upon activation of the device.
The present invention also provides a method for transporting a product that requires cooling. The method includes the steps of placing the product within a product cavity defined by at least top and bottom walls, placing a sorption cooling device in thermal communication with the cavity whereby the sorption cooling device is adapted to cool the cavity upon activation of the device, activating the sorption cooling device to initiate cooling of the cavity, transporting the product contained in the cavity from a first location to second location and removing the product from the cavity.